1,25 dihydroxyvitamin D3 (1,25(OH)2D3) stimulates calcium transport across and alkaline phosphatase and CaATPase activity of the intestinal brush border membrane. The purpose of the proposed research is to determine the mechanisms by which 1,25(OH)2D3 exerts these effects. I will examine whether 1,25(OH)2D3 stimulates calcium transport across the brush border membrane by a mechanism independent of new protein synthesis and different from the stimulation of alkaline phosphatase and CaATPase activity. I will evaluate the ability of cyclic AMP and calcium to mediate the effects of 1,25(OH)2D3 on these brush border membrane functions. The ability of 1,25(OH)2D3 administered in vivo to stimulate calcium uptake, alkaline phosphatase and CaATPase in subsequently isolated brush border membrane vesicles from chick duodenum will be determined. The effects of protein synthesis inhibitors on these 1,25(OH)2D3 stimulated events will be examined. The appearance of new proteins in the SDS polyacrylamide gel electrophoresis (SDS-PAGE) protein profiles of brush border membrane after 1,25(OH)2D3 administration will be correlated with changes in function of the membrane. Membrane protein phosphorylation will be evaluated by autoradiography of SDS-PAGE protein profiles of brush border membranes incubated with gamma 32P ATP. The influence of 1,25(OH)2D3 on membrane protein phosphorylation will be correlated to changes in membrane function. The ability of cAMP and calcium in vitro to mimic the effects of 1,25(OH)2D3 in vivo on calcium uptake, alkaline phosphatase, CaATPase and membrane protein phosphorylation will be determined. A role for calmodulin and the vitamin D dependent calcium binding protein in regulating any or all of these brush border membrane functions in the presence of calcium will be especially sought.